This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Qiutang Li, PI The long-term goal of this project is to elucidate the cellular and molecular mechanism by which IKKalpha exerts its effects on epidermal homeostasis. IKKalpha is a subunit of IKK complexes in NF-kappa B signaling pathway. IKKalpha knockout mice die at birth from the skin defects associated with increased proliferation and impaired terminal differentiation in keratinocytes. The function of IKKalpha in keratinocytes is independent from its kinase activity and NF-kappa B signaling pathway. The mechanism by which the IKKalpha regulates keratinocyte proliferation and differentiation remains unclear. In the present studies, we will test the hypothesis that IKKalpha regulates keratinocyte cell cycle and functions as a tumor suppressor gene in skin. Specifically, the following questions will be addressed: (1) What are the roles of the IKKalpha in regulation of the keratinocyte cell cycle and cell cycle checkpoint? (2) What are the IKKalpha-interacting proteins in keratinocyte? (3) How do those interacting proteins participate in the IKKalpha signaling in the keratinocytes? (4) Does IKKalpha function as a tumor suppressor in skin? Cell cycle analysis and functional studies will be performed in the primary keratinocytes isolated from either wild-type or the IKKalpha deficient embryos at embryonic day 18.5 using a combination of genetics, cytological, and biochemical approaches. The data that have been generated from IKKalpha immunoprecipitation and mass spectrometry will be further validated and characterized to understand the IKKalpha function at a molecular level. We will examine skin tumor susceptibility and metastatic potential in IKKalpha+/- mice exposed to mutagenic carcinogen and check the loss of heterozygosity frequency at the IKKalpha locus in IKKalpha+/- mouse tumors. The knowledge will be important for elucidating clinically relevant problems such as skin cancers.